Reflecting the scarcity of population-based data on Heart Rate Variability (HRV), the aims of the proposed study are to (a) examine the role of HRV as a predictor of fatal and nonfatal coronary heart disease (CHD) over a six-year follow-up of a bi-ethnic cohort; on the six-year progression of carotid atherosclerosis measured by B-mode ultrasound; and on the incidence rate of hypertension; and (b) to study the effect of elevated fasting insulin, glucose, diabetes mellitus, and other metabolic abnormalities on changes in HRV over the course of nine years in this cohort. The study will be conducted as a companion to the NHLBI-supported Atherosclerosis Risk in Communities (ARIC) study. Its population-based cohort of 15,800 black and white men and women was first examined in 1987-1998, followed by yearly contacts and re-examinations every three years. The investigators propose to build on the data collected by the ARIC investigators by retrieving and processing beat-to-beat heart rate data collected for a different purpose at baseline; by collecting 5 minutes of beat-to-beat heart rate data during the third ARIC follow-up examination (Visit 4) in 1996-1998; and by deriving fully comparable time, and frequency domain HRV indices from the baseline and the nine-year follow-up examinations on the 13,000 members of the ARIC cohort expected to take part in the latter (Visit 4). Through pilot studies on a sample of ARIC records the investigators state that they have demonstrated that: (a) it is feasible and informative to apply HRV analysis to these short heart rate records; (b) comparable HRV estimates can be obtained from baseline examination records and the data collection protocol to be used in Visit 4; (c) their intra- and inter-operator reliability coefficients for processing the HRV indices are >=0.95; and (d), that the High Frequency component of HRV is inversely associated with prevalent MI, diabetes mellitus and fasting serum insulin/glucose in individuals not diagnosed as diabetics. The investigators state that this study will provide a cost-effective opportunity to ascertain -- at the population level -- the natural history of HRV; the influence of various metabolic abnormalities on the temporal change in autonomic function; and the role of autonomic function in predicting the incidence of CHD and the progression of carotid atherosclerosis measured by B-Mode ultrasound.